Rotary cutting bit with material-deflecting ledge

ABSTRACT

A cutting bit includes a body having a front surface and a side surface, the side surface including a shoulder below the front surface and extending substantially perpendicular to a central axis of the body, and a ring that is harder than the body attached to the body at a front surface of the shoulder. Wear life of the cutting bit is enhanced by maintaining particular dimensional relationships regarding the position of the ring on the body, and the diameter of portions of the body.

BACKGROUND AND SUMMARY

The present invention relates to cutting tools used to cut through softground or through relatively soft material that has been laid on theground, such as asphalt roadways.

Mining, excavating, and road resurfacing operations are typicallyperformed by forcing rotary cutting bits through the material being cut.The cutting bits are mounted on a driven support, such as a rotary drum,fixed beam, or the like to be forced through the material. A typicalcutting bit comprises a hard cemented carbide tip that is brazed to thefront surface of a steel shank. The shank is to be mounted in a holderby means of a retainer sleeve which permits the bit to rotate freelyrelative to the holder about the bit's center axis, while beingrestrained against axial dislodgment from the holder. Due to beingfreely rotatable, the tip is basically self-sharpening.

It should be understood that cutting mechanisms of the type describedabove have been used to cut through hard materials, such as rock andice, in addition to cutting through softer materials such as asphalt.During the cutting of rock, the highest rate of bit wear occurs at thecarbide tip, so the wear life of the bit is determined by the carbidetip. However, during the cutting of relatively softer material, such asasphalt, coal, and salt, the highest rate of wear occurs at the shank,i.e., erosion caused by cut asphalt rubbing and impacting against theshank. Thus, when cutting asphalt during a road resurfacing operation,the wear life of the cutting bit is determined by the shank.

It would be desirable to provide a cutting bit that has an increasedwear life when used for cutting softer materials such as asphalt.

Disclosed in U.S. Pat. No. 4,725,098, which is incorporated byreference, is a cutting bit in which a groove is machined in a taperingside surface of the bit head closely behind a carbide tip mounted in thebit head. Hardfacing is deposited into the groove to form anerosion-resistant annular ring which can be flush with, or projectslightly radially beyond, the side surface. Despite being formed of hardmaterial, the ring will be subjected to considerable erosion by cuttingsand thus will have a somewhat limited life.

U.S. patent application Ser. No. 10/058,387, filed Jan. 30, 2002,entitled Rotary Cutting Bit with Material-Deflecting Ledge, naming KentPeay and Timothy J. Shean as inventors, which is incorporated byreference, discloses a cutting bit having a tapered side surface with aledge projecting from the tapered surface. The ledge can be integralwith the rest of the bit body or formed as a separate ring held on thebody. The ledge is of sufficient diameter relative to the portion of thebody above it that material cut tends to accumulate on the ledge andshields the body material underneath from erosion. However, it has beenfound that the ledge in such a cutting bit is highly prone to wear.

It would be desirable to provide a cutting bit with an erosion-resistantstructure which has an enhanced life. It would also be desirable toprovide a cutting bit that is simple to manufacture and involvesrelatively few manufacturing operations.

In accordance with an aspect of the present invention, a cutting bitincludes a body having a front surface and a side surface, the sidesurface including a shoulder below the front surface and extendingsubstantially perpendicular to a central axis of the body, the bodybeing no larger in diameter above the shoulder than at the shoulder, anda ring that is harder than the body attached to the body at a frontsurface of the shoulder.

In accordance with another aspect of the present invention, a cuttingbit includes a body having a front surface and a cylindrical sidesurface portion, the cylindrical side surface portion including ashoulder below the front surface and extending substantiallyperpendicular to a central axis of the body, and a ring that is harderthan the body attached to the body at a front surface of the shoulder. Adistance between the front surface and a top of the ring divided by adistance between the front surface and a bottom surface of the body is0.15 to 0.5.

In accordance with yet another aspect of the present invention, acutting bit includes a body having a front surface and a cylindricalside surface portion, the cylindrical side surface portion including ashoulder below the front surface and extending substantiallyperpendicular to a central axis of the body, a cutting tip attached tothe front surface, and a ring that is harder than the body attached tothe body at a front surface of the shoulder. A diameter of a bottom ofthe cutting tip divided by the diameter of the body at the bottom of thecuffing tip is 0.72 to 0.95.

In accordance with yet another aspect of the present invention, acutting bit includes a body having a front surface and a cylindricalside surface portion, the cylindrical side surface portion including ashoulder below the front surface and extending substantiallyperpendicular to a central axis of the body, a cutting tip attached tothe front surface, and a ring that is harder than the body attached tothe body at a front surface of the shoulder. A diameter of the cuttingbit divided by an outside diameter of the ring is 0.60 to 0.80.

In accordance with yet another aspect of the present invention, acutting bit includes a body having a front surface and a side surface,the side surface including a first shoulder below the front surface andextending substantially perpendicular to a central axis of the body, thebody being no larger in diameter above the first shoulder than at thefirst shoulder, and a second shoulder below the first shoulder, the bodybeing no larger in diameter above the second shoulder than at the secondshoulder, and a first ring and a second ring attached to the body at afront surface of, respectively, the first shoulder and the secondshoulder.

In accordance with still another aspect of the present invention, acutting tip for being attached to a cutting bit includes a base portion,a tip portion, the tip portion being generally convex in shape, and aside portion extending between the base portion and the tip portion, theside portion being generally concave in shape.

In accordance with still another aspect of the present invention, acutting bit includes a cutting tip having a base portion, a tip portion,the tip portion being generally convex in shape, and a side portionextending between the base portion and the tip portion, the side portionbeing generally concave in shape and intersecting with the tip portionat a junction. The cutting bit also includes a body having a front faceto which the cutting tip is attached, a bottom portion, and a shoulderbelow the front surface and extending substantially perpendicular to acentral axis of the body, and a ring that is harder than the bodyattached to the body at a front surface of the shoulder. An imaginarycone is defined by the junction and the bottom portion and the ring isdisposed inside of the cone.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and advantages of the invention will become apparent fromthe following detailed description of preferred embodiments thereof inconnection with the accompanying drawings in which like numeralsdesignate like elements and in which:

FIG. 1 is a side elevational view of a rotary cutting bit according toan embodiment of the present invention;

FIG. 2 is a side elevational view of a rotary cutting bit according toan embodiment of the present invention showing an accumulation of cutmaterial on the bit; and

FIG. 3 is a side elevational view of a rotary cutting bit according toanother embodiment of the present invention.

DETAILED DESCRIPTION

A cutting bit 21 according to an embodiment of the present invention isshown in FIGS. 1 and 2. The cutting bit 21 includes a body 23 having afront surface 25 and a side surface 27. The side surface 27 includes ashoulder 29 below the front surface 25 and extending substantiallyperpendicular to a central axis of the body. A cutting tip 31 ispreferably attached to the front surface 25, usually by brazing, thecutting tip preferably being harder than the body 23.

A ring 33 that is preferably harder than the body 23 is attached to thebody at a front surface 35 of the shoulder 29, such as by brazing. Thebody 23 is preferably no larger in diameter above the shoulder 29 thanat the shoulder and, preferably, at least a portion 37 of the sidesurface 27 of the body 23 is cylindrical, more preferably circularlycylindrical, above the shoulder 29 so that a ring having a circularinside diameter can be slid over the body to the shoulder. Because thebody 23 is preferably no larger in diameter above the shoulder 29 thanat the shoulder, it is not necessary to incur machining costs formachining a groove in the body. Also, the body 23 can be cold formed.The ring 33 is preferably positioned above the shoulder 29 and brazed tothe body 23 in the same operation, which can minimize manufacturingcosts, particularly when compared with bits wherein a groove must beformed. If desired or necessary, however, the shoulder 29 can be part ofa groove in the side surface and the ring can be, for example, a splitring that is held in place by upper and lower surfaces of the groove.The ring 33 is illustrated as being a substantially circular shape,however, it will be appreciated that the ring can be any desired shape,such as hexagonal, octagonal, etc.

In the cutting bit 21′ shown in FIG. 3, the body 23′ includes a secondshoulder 39 below the first shoulder 29. Again, the body 23′ ispreferably no larger in diameter above the second shoulder 39 than atthe second shoulder to facilitate sliding a second ring 41 over the bodyto the second shoulder where it is attached to the body at a frontsurface of the second shoulder. Again, if desired or necessary, however,the shoulder 39 can be part of a groove in the side surface and the ring41 can be, for example, a split ring that is held in place by upper andlower surfaces of the groove.

A distance A between the front surface 25 and a top 43 of the ring 33divided by a distance B between the front surface and a bottom surface45 of the body is preferably 0.15 to 0.5. It is intended that materialbeing cut will accumulate on the ring 33 and the material will preventerosion of the body 23 between the ring and the cutting tip 31 bydeflecting further material. A flange 47, which is preferably integralwith the body, is preferably provided at the bottom of the body 23. Cutmaterial tends to accumulate on the flange 47 in a manner similar to themanner in which material accumulates on the ring 33.

In the past, a wear pattern between a cutting tip and a bottom flange ona body would tend to approximate the “golf tee” shape shown by thedotted line X in FIG. 2. It has been found that providing the ring 33 ina region that would ordinarily be subject to significant erosion resultsin a substantially reduced volume loss of material from the body 23 andtends to approximate the double “golf tee” shape shown as the shadedarea Y in FIG. 2. While it is desirable to prevent body wear, it is alsodesirable to ensure that the ring 33 is at a sufficient distance fromthe cutting tip 31 to avoid a dulling of the cutting action, which canbe achieved by keeping the relationship between distance A and distanceB in the range of 0.15 to 0.5. If a second shoulder 39 and ring 41 areprovided as in FIG. 3, it is preferred that a distance A′ between thefront surface 25 and a top 49 of the second ring 41 divided by thedistance B between the front surface and a bottom surface 45 of the bodyis, as with the first ring 33, 0.15 to 0.5. This tends to place both thefirst ring 33 and the second ring 41 in what would otherwise be a regionof maximum erosion on the body 23.

A diameter C of the cutting tip 31 divided by a diameter D of the body23 at the bottom of the cutting tip is preferably 0.72 to 0.95. Thefront surface 25 is preferably recessed to define a dam wall 51 in whichthe cutting tip 31 is attached by brazing. Purposes of the dam wall 49include preventing brazing liquid from flowing out from between thecutting tip 31 and the front surface 25 and acting as a stress relieverwhen the body 23 cools off. As C/D becomes closer to 1, the thickness ofthe dam wall 49 is reduced and less material is needed to form the body23. As C/D moves from 1 toward 0, the body 23 has more material and itsuseful life span tends to approach that of the cutting tip 31 made ofharder material.

The diameter C of the cutting tip 31 divided by an outside diameter E ofthe ring is preferably 0.60 to 0.80. As seen in FIGS. 1-3, the cuttingtip 31 preferably has a bottom surface 52 that is brazed to the frontsurface 25 inside the dam wall 49, a concave surface portion 53extending upwardly to a break point 55, and a tip portion 57 that isgenerally convex. As seen in FIGS. 2 and 3, an imaginary cone 59 extendsthrough a point 61 on the outer edge of the flange 47 and the breakpoint 55 to a point 63 above the tip portion 57 along the center axis ofthe body 23. It has been found desirable to keep all points on thecutting bit 21, including points on the ring 33, inside or at leastsubstantially inside of this cone 59. Points extending outwardly beyondthe cone tend to be too vulnerable to erosion. By keeping C/E in therange of 0.60 to 0.80, particularly when A/B is 0.15 to 0.50 and C/D is0.72 to 0.95, the outermost point on the ring 33 tends to fall on orinside of the cone 59 and is less subject to wear. The relationshipsdescribed above in connection with the cutting bit having only the ring33 are preferably also true for bits having two or more rings, e.g., thebit 21′ including the ring 41 shown in FIG. 3.

Although the present invention has been described in connection withpreferred embodiments thereof, it will be appreciated by those skilledin the art that additions, deletions, modifications, and substitutionsnot specifically described may be made without departing from the spiritand scope of the invention as defined in the appended claims.

1. A cutting bit, comprising: A body having a front surface and a sidesurface, the side surface including a shoulder below the front surfaceand extending substantially perpendicular to a central axis of the body,the body being no larger in diameter above the shoulder than at theshoulder; and a ring that is harder than the body attached to the bodyat a front surface of the shoulder. 2-26. (canceled)